Two simple methods of aquifer vulnerability assessment were used in this study: the GOD and AVI methods. The main purpose was to appraise their faithfulness as exploratory techniques, and their applicability to the scale of a small watershed. The study area was the Sordo River Basin (area: 50 km2), located in the Northeast of Portugal. To measure accuracy, model results were compared with vulnerability maps previously obtained for the basin, but using the standard DRASTIC model. Results of the GOD method were a map dominated by class "low vulnerability" where parameter O (overlying strata) imprinted its signature, very similar to the DRASTIC map but with smaller resolution. The method was considered valuable for exploration of primary factors of aquifer vulnerability (e.g. discrimination between water table and confined aquifers) but not for description of secondary factors (e.g. nuances in the degree of confinement). The application of the AVI method was proven inefficient because the resulting map indicated the presence of a single unrealistic class ("extremely high vulnerability"). The reason was that AVI results are evaluated on a logarithmic scale, which is appropriate for studies at regional scales where the settings are very diverse, but inappropriate for studies on the small watershed scale.
Groundwater vulnerability to pollution; aquifers; Sordo River; GOD; AVI
